In common English, what does “opening Pandora’s box” mean?

In common English, “opening Pandora’s box” means unleashing unforeseen problems. The idiom describes an action that creates many unexpected difficulties or consequences.

The expression comes from the Greek myth in which Pandora opens a container and releases troubles into the human world. Once released, the troubles cannot easily be gathered back up, so the phrase is now used for decisions whose consequences spread beyond what was intended.

The idiom is often applied to politics, technology, law, business, and personal disputes. It does not usually mean that the person literally discovers evil; it means that one act begins a chain of complications. The phrase can also suggest that the consequences are difficult or impossible to reverse.

The wording is based on the later “box” version of the story. Hesiod’s original account refers to a pithos, or large jar, but English usage made “Pandora’s box” the standard expression.